In collaboration with Professor Kraut's group and others, we have collected more than 300,000 intensity measurements on the parent and three heavy atom derivatives of the crystals of cytochrome c peroxidase. This has enabled us to solve the structure of this very interesting enzyme (T. Poulos et al., J. Biol. Chem. 255: 575-580 (1980)). Diffraction data at higher resolution (out to 1.8 A have been collected and a structure refinement is in progress. In the meantime we have started to collect data on the enzyme-substrate complex of this enzyme (compound I). Since the crystal of this complex is unstable at room temperature, data collection must be done at low temperature (about minus 20 degrees centigrade). In collaboration with Professor R. Salemme's group at the University of Arizona, we have solved the structure of cytochrome c' at 2.5 A resolution (P. Weber, et al, Nature, in press (1980)). A set of 1.7 A resolution data have been collected and a structure refinement is in progress. We have started a collaboration with Professor D. Eisenberg's group in UCLA to solve the structure of Ribulose Bisphosphate Carboxylase/Oxygenase (RuBPCase). Constituting 50% of the soluble protein of leaves, this enzyme is believed to be the most abundant on earth. RuBPCase initiates the Calvin cycle of photosynthesis by condensation of CO2 with ribulose bisphosphate. It also is a central element in photorespiration, functioning as an oxygenase.